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H. Nett
ESA/ESTEC, ENVISAT Programme Division
P.O. Box 299, NL-2200 AG Noordwijk
e-mail: hnett@jw.estec.esa.nl
ABSTRACT
The Michelson Interferometer for Passive Atmospheric Sounding will be one of the atmospheric payload instrument on
board ESA's polar orbiting ENVISAT. Sensing the Earth's limb emission in a wavelength range 4.15 ... 14.6 micrometers
it will allow detection of a large number of middle atmospheric constituents of primary interest for various disciplines of
atmospheric research. Besides generation of geolocated, fully calibrated limb radiance data (Level 1B products), abun-
dancy profiles of a set of primary target species, together with atmospheric pressure, temperature (Level 2 products) will
be systematically processed and disseminated in near real time. Whereas the development of the essential on-ground
algorithm components has been finalised work now focuses on the analysis of specific measurement scenarios that will
be required in conjunction with the various planned post-launch verification and characterisation tasks. The work is car-
ried out in a co-ordinated effort, involving expert teams already involved in earlier algorithm studies, and is supported
through a number of specific projects initiated in the frame of the ENVISAT Announcement of Opportunitiy (AO). The
primary tasks to be performed in the frame of the MIPAS CalVal project have been identified and an overall plan for their
implementation has been established.
INTRODUCTION
As one of the atmospheric instruments on board ENVISAT MIPAS will routinely sense the Earth's limb emission in the
mid-infrared and acquire radiance data in a total of 5 spectral bands ([1]). The mission concept foresees systematic pro-
cessing of MIPAS scene and calibration measurements up to fully calibrated, geo-located limb radiance data (Level 1B)
and vertical profiles of atmospheric pressure, temperarture and volume-mixing-ratios of the primary target species O
3
,
H
2
O, CH
4
, N
2
O, NO
2
and HNO
3
(Level 2). Prerequisites for a stable data acquisition and ground processing scenario are
a number of calibration, characterisation and diagnostics activities that will support the operation of instrument and
ground processor throughout the envisaged mission lifetime of four years. Moreover, the overall accuracies of geophysi-
cal parameters and associated information provided in the data products need to be evaluated and reported on, to allow
full and correct interpretation by MIPAS users. This includes, in particular, the compilation of total error budgets, taking
into account random and systematic contributions due to instrumental effects, characterisation uncertainties, in-flight ca-
libration errors or modelling/approximation errors induced by the on-ground processing algorithms. Whenever appropri-
ate ground processor functionalities and generated output parameters will be validated through intercomparisons with
correlative information, provided through reference measurements or other, non-ENVISAT information sources.
This paper will discuss, after a brief review of primary MIPAS data products, envisaged activities related to initial in-
flight calibration and characterisation. The strategy to verify critical components of the MIPAS Level 1B/2 processing
stages as well as the role of the various expert teams supporting the MIPAS CalVal project will be outlined.
REVIEW OF MIPAS DATA PRODUCTS
During routine operation MIPAS data will be recorded on board ENVISAT and downlinked typically once per orbit,
according to visibility of a receiving ground station. Each downlinked sequence will be converted into a so-called
Level 0 product that will form the basis for all further processing. The Level 1B stage of the Instrument Processing
Facility (IPF) performs the conversion of instrument raw data (scene, blackbody and deep space) and various auxiliary
input data into fully calibrated, geo-located radiance spectra. A number of supplementary parameters are computed and
included in the Level 1B product, to support the correct interpretation the further processing in the Level 2 component
([2]).
The Level 2 processing is based on the analysis of emission features of selected target gases from the Level 1B input data
and is performed in two stages, (1) retrieval of p, T profiles and (2) sequential retrieval of VMR profiles for the six target
species, using the pressure, temperature information retrieved in the first stage. Several auxiliary data are required that
control, e.g., the extraction / pre-processing of the Level 1B input data or provide atmospheric state parameters as used
by the iterative profile fit algortithm (see [3], [4]).
Tables 1
& 2 provide an overview of MIPAS data products and list some relevant performance parameters.
Table 1. MIPAS Level 1B product summary
PRODUCT
MIP_NL__1P
NAME
Geo-located, fully calibrated MIPAS limb emission spectra
DESCRIPTION
Measurement data:
Spectrally and radiometrically calibrated limb emission spectra in the 685 - 2,410 wavenumber range
5 bands: A: 685-970 cm
-1
, AB: 1,020-1,170 cm
-1
, B: 1,215-1,500 cm
-1
,
C: 1,570-1,750 cm
-1
, D: 1,820-2,410cm
-1
Annotation data:
Geolocation information, product confidence data, processing parameters, NESR data, offset calibration data
PRODUCT SIZE
approx. 310 Mbytes per orbit
COVERAGE
Line-of-sight (LOS) tangent height range:
8 km ... 53 km (typ.)
Pointing range (azimuth pointing relative to S/C velocity vector):
160
0
- 190
0
(rearward viewing)
75
0
- 110
0
(sideward viewing)
ACQUISITION
TIME
duration of an interferometer stroke (`sweep'):
~ 4.45 s
at high resolution (MPD = 20 cm)
~ 0.85 s
at low resolution (MPD = 2 cm)
GEOMETRIC
RESOLUTION
Instantaneous field of view (IFOV): 0.0523
0
(elevation)
0.523
0
(azimuth)
At LOS tangent point (effective):
3 km (vertical)
30 km (horizontal)
(rearward looking)
3 km (vertical)
60 km (horizontal)
(sideward looking)
Horizontal displacement between subsequent ele-
vation scan sequences (typ., rearward viewing):
approx. 400 km
SPECTRAL
RESOLUTION
0.031 cm
-1
... 0.035 cm
-1
(for high resolution setting; MPD = 20 cm)
RADIOMETRIC
ACCURACY
685 - 1,500 cm
-1
:
2 * NESR
T a
+ 5 % [true source spectral radiance]
1,570 - 2,410 cm
-1
:
2 * NESR
T
+ X % of [true source spectral radiance],
(X to be linearly interpolated between 2 at 1,570 cm
-1
and 3 at 2,410 cm
-1
)
a. Noise equivalent spectral radiance when the instrument is viewing a blackbody source at temperature T.
AUXILIARY
DATA
Instrument characterisation data, LOS calibration data, parameters controlling spectral calibration & instrument
lineshape retrieval, orbit state vector & attitude information, others.
A description of the MIPAS data products, corresponding auxiliary input data and of the underlying processing algo-
rithms is provided in ENVISAT Simulated Products /MIPAS volume (CD-ROM) [6].
COMMISSIONING PHASE CALIBRATION & VERIFICATION TASKS
Instrument & Level 1B related tasks
The initial period of MIPAS in-orbit operation will be dedicated to a number of specific checks and calibration measure-
ments, in order prepare the instrument for the routine exploitation. The envisaged activities can be grouped as follows:
·
Switch-on and data acquisition phase (SODAP) tasks
- stabilisation of the instrument's thermal environment and initial `switch on'
- verification of the instrument's full functionality, commandability in various configurations and of the communica-
tion between instrument, satellite and on-ground facilities
·
Initial instrument characterisation and optimisation of calibration scenario
- initial instrument related performance analysis (noise equivalent spectral radiance (NESR), instrument
lineshape (ILS), line-of-sight (LOS) mispointing, ...)
- drift analyses and optimisation of radiometric and spectral calibration cycles
- re-computation and uplink of on-board settings & control tables
- acquisition of initial calibration data for use in Level 1B processing
- generation of a preliminary L1B data set for use in early Level 2 algorithm analyses
- identification and correction of potential inconsistencies in the Level 0 to 1B processing stage
·
full Level 1B related characterisation & validation
- update of in-flight characterisation data base and generation of full set of Level 1B auxiliary data
- optimisation of specific Level 1B algorithm settings, to ensure correct performance and a stable output of the ground
processor
- initialisation of routine performance monitoring functions, i.e., definition of settings used on ground for routine
instrument health checks and to detect potential degradations with respect to the initial performance
- assessment of total Level 1B error budgets including instrument and algorithm induced inaccuracies.
Table 2. MIPAS Level 2 product summary sheet
PRODUCT
MIP_NL__2P
NAME
Atmospheric pressure, temperature data, constituents profiles of primary MIPAS target species
DESCRIPTION
Measurement data:
Geolocated, vertical profiles of p, T, O
3
, H
2
O, CH
4
, N
2
O, NO
2
, HNO
3
, tangent height correction data, profile
variance/covariance data, concentration and column density profiles, fitted continuum absorption and radiome-
tric offset parameters
Annotation data:
Product confidence data, residual spectra, microwindow&occupation matrix data, evolution of state parameters
during iterative fit procedure, processing parameters
PRODUCT SIZE
approx. 8.2 Mbytes per orbit
COVERAGE
Global coverage, i.e. mapping of the Earth's upper Troposphere and Stratosphere at all latitudes and longitudes
GEOMETRIC
RESOLUTION
Vertical resolution of p, T and VMR profiles:
approx. 3 km
Horizontal resolution of p, T and VMR profiles:
approx. 400 km ... 500 km (along track)
AUXILIARY
DATA
Spectroscopic data, pre-tabulated cross-sections, microwindows & occupation matrix data, validation thresh-
olds, initial guess p, T and trace gas VMR profiles, a priori pointing information, processing setup / configu-
ration parameters
Level 2 related tasks
In addition to the above listed tasks specific analyses are foreseen during commissioning phase that focus at the early ver-
ification of vital Level 2 algorithm components and auxiliary input data. These checks shall serve to identify inconsisten-
cies in the L1B to L2 processing chain and to implement necessary corrections in affected algorithm components at a
very early stage. This will ensure an improved performance of the Level 2 stage and the availability of a stable output
data set for use in the different geophysical validations projects ([7]). These initial checks will be supported by dedicated
characterisation measurements the results of which will be analysed according to pre-defined procedures. Use will be
made of a suit of diagnostic tools specifically developed for this purpose.
The early Level 2 analysis work will focus on:
1. instrument modelling: check of validity of essential modelling/performance parameters, in particular:
- ILS parameters, including spectral dependency
- NESR levels, magnitude and spectral correlation
- representation of field-of-view (FOV) pattern and FOV convolution model
- modelling of LOS pointing perturbations (used as a priori input in p, T retrievals)
- assumptions on residual radiometric and spectral calibration errors in Level 1B processing
2. forward modelling: checks of critical atmospheric sub-models and parameters, in particular:
- volume-mixing-ratio (VMR) profiles of species interfering in selected retrieval spectral intervals (`microwindows')
- initial guess profile data
- impact of non-modelled high altitude line emissions (non-local thermodynamic equilibrium (NLTE) effects)
- vertical and spectral correlations of non- or poorly modelled atmospheric continuum contributions
3. pressure, temperature retrieval stage: checks of retrieved pressure, temperature profiles through
- intercomparisons with external data (e.g., geopotential, temperature fields from ECMWF analyses)
- consistency check using information from the MIPAS line-of-sight (LOS) pointing system and the assumption of
hydrostatic equilibrium in the observed target atmosphere
4. VMR retrieval stage: checks of retrieved VMR profiles through intercomparisons with external data, for a subset of
target species (e.g., H
2
O derived from ECMWF analyses)
5. critical parameter tuning: optimisation of performance critical settings, e.g.
- parameters related to Level 1B data extraction/pre-processing
- iteration feedback and threshold parameters
- settings controlling the choice of retrieval unknowns.
6. spectroscopic data base: initial inspection of Level 1B radiances in retrieval microwindows, and of residual radiance
spectra generated by the Level 2 algorithm, for completeness of selected line data and potential systematic errors
7. overall processor performance: analysis of specific Level 2 quality parameters, allowing to identify sources of exces-
sive systematic errors in fit results, numerical instabilities, excessive CPU loads, etc.
Refer to [3], [4] for a more comprehensive discussion of the various sub-models.
TEAM COMPOSITION AND ASSIGNMENT OF TASKS
The MIPAS Cal/Val team is composed of several study groups the majority of which have been involved, as so-called
Expert Support Laboratories (ESL's), in earlier work on instrument characterisation and algorithm development. A num-
ber of specific tasks will be carried out by expert groups involved in the CalVal activity through project proposals submit-
ted in the frame of the ENVISAT Announcement of Opportunity (AO). Table 3 list institutes/companies involved in the
MIPAS CalVal work and summarises key tasks assigned to them.
Table 3. Overview of MIPAS calibration and algorithm verification activities
Involved institutes /
companies
Task
AO project
Instrument and Level 1B related work
ABB BOMEM Inc.,
ASTRIUM GmbH,
ESA/ENVISAT project
team
· characterisation & optimisation of instrument parameters (e.g., analog & digital
signal processing)
· characterisation of performance parameters (detector non-linearity, NESR levels,
radiometric accuracy, drifts in radiometric gain / offset data, ILS shape & stability,
spectral axis linearity, ...)
· characterisation of systematic LOS mispointing (bias & orbit harmonics)
· optimisation of settings for routine calibration measurements (spectral resolution,
repeat cycles for deep space calibration, ...)
· generation of template data for L1B validation functions
· initialisation of long-term performance monitoring functions
· routine generation and maintenance of L1B auxiliary data bases
- / -
FZ-IMK, DLR, IAA
· verification of NESR data reported in MIPAS L1B products
· Verification of absence of noise correlation in calibrated MIPAS spectra
· Verification of ILS parametrisation as implemented in IECF
· Verification of ILS stability and characterisation of tangent altitude dependencies
· spectral calibration analysis and characterisation of residual errors in L1B data
· characterisation of spurious signals in deep space calibration measurements
AO#145
("INFLIC")
DLR, FZ-IMK
· analysis of noise sources contributing to the overall NESR levels observed in L1B
spectra
· verification of detector non-linearity correction scheme implemented in MIPAS
L1B algorithm by means of alternative analyses
· assessment of L1B inaccuracies induced by erronous characterisation parameters
· verification of ILS retrieval algorithm by means of independent modelling
· characterisation of systematic error sources due to simplified modelling in L1B /
IECF algorithms
AO#652
("IRAC")
Universities of Leicester,
Canterbury and
Hampton, LPM
validation of MIPAS Level 1B radiance data in selected spectral intervals (microwin-
dows) by means of direct radiative transfer modelling
AO#357
("CUTLSOM")
all teams
identification of potential errors in Level 1B algorithm and recommendations for
enhancements of critical components and the auxiliary input data
ABB BOMEM Inc.,
DJO GmbH
implementation & verification of Level 1B algorithm changes or auxiliary data
enhancements as resulting from AO project and IECF activities
-/-
Level 2 related work
IROE-CNR,
U. of Bologna,
ISM-CNR,
Universities of Oxford &
Leicester,
FZ-IMK, LPM
· in-depth analysis of specific L2 product parameters and identification of potential
algorithm or auxiliary data induced errors
· verification of spectroscopic line data base through inspection of residual radiance
errors in L2 fit results
· identification and quantification of systematic error sources in L2 results as
induced, e.g., through
- erronous auxiliary data (e.g., spectroscopic line parameters, interfering gas
concentrations)
- incorrect atmospheric modelling (neglection of spatial gradients, deviations
form hydrostatic equilibrium, ...)
- incorrect instrument modelling (instantaneous field of view, ILS, LOS pointing
fluctuations).
- / -
IROE-CNR, U. of Bolo-
gna, ISM-CNR, U. of
Oxford, U. of Leicester,
FZ-IMK, LPM,
ASTRIUM GmbH,
ESA/ENVISAT project
team
· generation of intermediate L2 results for use by ESL / AO project teams
· characterisation of the overall L2 algorithm performance
· enhancement of L2 processing parameters through iterative tuning of algorithm
sub-components
· acquisition and re-formatting of L2 related auxiliary data bases generated external
to the IECF
· verification of overall consistency of auxiliary data bases, taking into account inter-
dependencies
· initialisation of long-term performance monitoring and validation functions
- / -
OVERALL TIMELINE
As outlined in the previous section, both, Level 1B and Level 2 related work will be carried out during the commissio-
ning phase, whereas the L2 analyses will depend on the availability of a preliminary L1B data set. Pre-requisites for a
successful completion of these tasks are the optimisation of instrument performance and the overall calibration scheme.
The early commissioning phase activities will therefore focus on acquisition and analysis of dedicated characterisation
measurements that allow to implement a stable measurement scenario and to generate the required ground processor out-
put. It is envisaged to complete the optimisation of instrument settings (signal processing, LOS pointing correction
tables, ..) and the - preliminary - characterisation of key parameters as required by the Level 2 stage (e.g., NESR, radio-
metric accuracy, ILS, spectral calibration) within the initial four months of ENVISAT's in orbit operation.
The actual Level 2 related analysis work will require the instrument to be operated in stable `nominal' mode for specific
periods (typically covering several orbits), with periodic limb measurements and radiometric calibration sequences. Data
acquired during these intervals will be processed by the MIPAS PF and the generated Level 1B and Level 2 data products
will be delivered to the involved expert teams.
The sequence of planned instrument and algorithm related characterisation and verification activities is illustrated in
Fig. 1
. Also indicated are the commissioning workshop and the validation review workshop, scheduled towards the end
of commissioning phase and end of initial validation activites, respectively.
Table 3. Overview of MIPAS calibration and algorithm verification activities (... continued)
Involved institutes /
companies
Task
AO project
Level 2 related work
IAA, FZ-IMK, LPM
· verification of upper atmospheric CO
2
mixing ratios as used in routine L2 pressure,
temperature retrievals
· characterisation of Non Local Thermodynamic Equilibrium (NLTE) induced radi-
ances in operational MIPAS retrieval microwindows
· quantification of errors in L2 results due to neglection of NLTE effects for all
MIPAS target species
· recommendations for enhanced selection scheme for L2 retrieval microwindows
and for the assessment of systematic errors in routine L2 retrievals
AO#304
Universities of Leicester,
Canterbury, Hampton,
LPM
validation of MIPAS Level 1B radiance data in selected spectral intervals (microwin-
dows) by means of direct radiative transfer modelling
AO#323
all teams
· identification of potential error sources in the MIPAS IPF / Level 2 component
· re-assessment of systematic error components and compilation of total L2 error
budgets
· consultancy during interpretation of MIPAS L2 key results in support of the correl-
ative measurement and geophysical validation activities
· recommendations with respect to enhancements of the overall Level 0 to 2 process-
ing scheme and related auxiliary input data
ASTRIUM GmbH,
DJO GmbH
implementation & verification of Level 2 algorithm changes and updated auxiliary
data.
- / -
EARLY IN-FLIGHT INSTRUMENT OPERATION & DATA CIRCULATION
Prior to realisation of dedicated calibration and characterisation measurements various instrument settings and control
parameters need to be computed and uploaded to the instrument. Once the instrument has been configured the actual
command sequences to activate a particular measurement need to be uplinked, making use of previously optimised time-
line parameters. Likewise, as soon as the actual measurement sequence has been acquired the instrument data received on
ground need to be converted into a data product (e.g., a Level 1B file) and transferred to the site that will carry out the
analysis. The implementation of such dedicated measurements requires a number of supporting on-ground facilities, in
particular:
·
Mission Planning Tool [ MIPAS-MP ]
Computation of on-board control parameters (e.g., pointing tables, timeline parameters, ...) for user requested scene /
calibration measurements
·
Flight Operation Segment [ FOS ]
Uplink of instrument control parameters, scheduling of command execution, analysis of orbit / attitude information
·
Paoload Data Handling Station Kiruna / ESRIN [ PDHS-K / -E ]
Host of the MIPAS Processing Facility, will acquire instrument data and generate L1B & 2 data products
·
Archiving Facility (ARF) & Inventory (INV)
Archiving of all MIPAS data products (L0, L1B, L2) and auxiliary data & inventory data base, will display contents
of all archived ENVISAT data and supply details required for product ordering
·
User Service Facility [ USF ]
Interface to ESA external data users, accepts product orders and provides processing status information to users
·
Instrument Engineering Calibration Facility [ IECF ]
Processing of routine and dedicated calibration, characterisation measurements, performance monitoring, generation
of L1B / L2 auxiliary input data used in the PDHS. During early in-orbit operation the IECF will generate specific
results required by the CalVal groups for dedicated analysis work and, in turn, acquire data generated by them (e.g.,
updated auxiliary data bases or processor settings) for re-injection in the MIPAS processing chain.
Fig. 1.
Overall schedule of MIPAS Cal/Val activities.
L1B algorithm & product validation,
update of characterisation data
L2 algorithm char.
& verification
analysis of correlative
measurements
(balloon,
aircraft, ground-based ...)
geophysical validation
preliminary
L1B data set
release L1B
data product
prelim. vali-
dated L2 data
Pre-launch algorithm
validation, performance
analyses, preparation of
tools
Preparatory activities
Launch
instrument
`switch-on'
optimisation of
cal. scenario & on
board tables
L1B related char-
acterisation
Validation
Workshop
Comm.
Phase Work-
shop
L +
4 w
time
early L2 related
checks
L +
4 m
L +
6 m
L +
9 m
SODAP
related
analyses
L: date of Envisat
launch
w: weeks
m: months
In addition to these ESA operated facilities a dedicated validation data centre, the NILU data base, will be installed and
maintained throughout the full duration of the ENVISAT CalVal activities. The NILU centre will host all correlative
results generated for all ENVISAT instruments by the various calibration/validation teams and allow all involved groups
to access data generated by the other teams.
An overview of the various ground facilities supporting the MIPAS CalVal activities, and of the primary data flows is
given in Fig. 2.
CONCLUSIONS
The MIPAS ground processing concept foresees routine generation, dissemination and archiving of raw instrument
(Level 0) data and higher level (1B &2) data products. A sound baseline has been established for both the Level 1B and 2
stages including the strategy for generating the auxiliary input data. Current work focuses on pre-launch validation of
critical algorithm components and auxiliary data, and on the definition of dedicated calibration & characterisation mea-
surements to be performed during the commissioning phase. The analysis and interpretation of acquired MIPAS data will
be performed in the IECF as well as in various ESA external institutes involved in the ENVISAT CalVal project. The
access to ENVISAT data and the implementation of updated L1B/L2 algorithm input data generated by CalVal groups
will be facilitated through various centres within the ENVISAT ground segment. The circulation of results produced in
the frame of the CalVal project will be supported by the NILU data centre, allowing all involved teams to access correla-
tive information already at a very early stage during the instrument's in-orbit operation.
ACKNOWLEDGEMENTS
The author is grateful to all teams involved in the MIPAS Level 1B / Level 2 algorithm work (BOMEM Inc., IROE-CNR,
FMA, Univ. of Bologna, ISM, FZ-IMK, LPM, Univ. of Oxford, Astrium GmbH) for their valuable contributions
throughout all phases of the project. Special thanks to the principle investigators who have, in the frame of the ENVI-
SAT-AO, provided inputs for setting up a MIPAS validation plan, and who have taken the challenging commitment of
supporting the in-flight calibration / validation project during the early phases of ENVISAT's in-orbit operation.
Fig. 2.
Primary ground facilities and main data flows during early MIPAS in-flight operation and CalVal activities
(simplified).
MIPAS pro-
ducts (L1B, L2,
aux. data)
Flight Opera-
tion Segment
[ FOS ]
Payload Data
Handling Station
[PDHS-K/-E ]
Mission
Planning
[MIPAS-MP ]
Instrument Engineering
Calibration Facility
[ IECF ]
Archiving
Facility [ARF]
Inventory [INV ]
User Service
Facility
[ USF ]
orbit analy-
sis data
updated instru-
ment parame-
ters / timelines
Laboratories, processing sites of MIPAS
Calibration / Validation teams
NILU
1
Validation
Data Centre
product
order
requests for specific
char. measurement
correlative
results,
reports
updated
aux. data
unprocessed
cal. /char. data
ESA
operated
facilities
external
facilities
processed
MIPAS data
specific
processed
data sets
updated aux.
data, tuning
parameters
updated
on-board
settings
1
Norwegian Institute for Air Research
REFERENCES
[1] Endemann, M., "MIPAS Instrument Concept and Performance", ESAMS `99, Conference Proceedings.
[2] Lachance, R.L., "MIPAS Level 1B Algorithm Technical Baseline Document: An Overview", European Symposium
on Atmospheric Measurements from Space (ESAMS `99), ESTEC/Noordwijk, 18-22 January 1999, Conference Pro-
ceedings.
[3] Carli, B. et al., "MIPAS Level 2 Algorithm", ESAMS `99, Conference Proceedings.
[4] Ridolfi, M. et al., "Optimised forward model and retrieval scheme for MIPAS near-real-time data processing",
Applied Optics, Vol. 39, No. 8, March 2000.
[5] Nett. H., "MIPAS Data Products", ESAMS `99, Conference Proceedings.
[6] ESA, "ENVISAT Simulated Products/MIPAS Volume", CD-ROM, to be distributed at ERS-Envisat Symposium,
Gothenburg, 16-20 Oct. 2000.
[7] Envisat CalVal Team, "ENVISAT Calibration and Validation Plan", ESA document PO-PL-ESA-GS-1092,
issue 1.02.
Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry